In a composting toilet feces and toilet paper compost with a “bulking agent” like sawdust cover the poop to create air gaps for aerobic bacteria to break down the material. This process is the same as for a household food scrap compost. Urine can be diverted out of the toilet, but it is not necessary. If urine is included more sawdust is added to soap up excess liquid. Composting toilets are often used in areas with easy access to wood shavings, leaf duff, or other suitable cover. The finished product is a moist humus similar to garden compost.
In a dry toilet ash or lime mixed with dry soil are added to create a dehydrating environment for breakdown and die off of pathogens. Dry toilets are often used in arid, dry climates where lime and ash are more available than sawdust. Toilet paper can not be added to a dry toilet, it is usually burned or buried. Pathogens typically die off more quickly in the dry, high pH environment of a dry toilet. The finished product can be used as a soil amendment and resembles instant coffee.